2001 Mazda 626 Code P0400

Hi, have mazda and I have check engine light on. Comes on every 30-40 after I reset it. The code P0400 reads: Exhaust Gas Recirculation Flow Malfunction.
I changed EGR valve, cleaned EGR ports (appeared to be clean), changed EGR boost sensor, changed spark plugs, plug wires but the code P0400 keeps coming back after a reset. Went to the dealer, they said it is Boost sensor but it wasn't, I replaced it but the code came back. They gave my money back for the diagnostics and said that it is possibly wiring problems and to test is $100 + TAX but no guarentee. Really frusterating, don't know what to do. Need to pass emission test for NY state. Please help!

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Sunday, October 31st, 2010 AT 10:58 AM

1 Reply

KHLOW2008

EXPERT

42,231 POSTS

Hi dpetrow,

Here are the diagnostics for the trouble codes.

DTC P0400: EGR FLOW MALFUNCTION
Condition
DTC is set when intake manifold pressure is to high or to low when EGR is turn on and off.

Diagnosis & Repair Procedure

1. Perform DTC confirmation procedure. Check for DTCs during KOEO or KOER self-test. If DTC P0400 is present, go to next step. If DTC P0400 is not present, problem is intermittent.

2. Check EGR boost solenoid valve connector connection. Repair as necessary and check for any other DTC during KOEO or KOER self-test. If any other DTCs are present, go to appropriate test. If no other DTC is present, go to next step.

3. Check for vacuum leaks in hoses connected to MAF sensor, hoses connected to throttle body, intake manifold gasket, PCV system, other vacuum hoses (disconnected) or loose engine dipstick. Also check for exhaust leaks at flanges or gaskets. Repair as necessary and go to step 17 . If no leaks are found, go to next step.

4. Using compression gauge, check cylinder compression. Minimum cylinder compression should be 119 psi (8.4 kg/cm2 ) at 300 RPM and maximum difference between cylinders should be 28 psi (2.0 kg/cm2 ). If cylinder compression is not okay, repair engine as necessary and go to step 17 . If compression is okay, go to next step.

5. Turn ignition on. Listen for click (initialization noise) from EGR valve. EGR valve initialization is closing action of EGR valve before and after engine is turn on and off. If noise can be heard, go to step 11 . If noise cannot be heard, go to next step.